Heart disease is a major cause of early death throughout the world. One treatment approach is to incorporate an implantable heart assist pump that can work in parallel with the natural heart to provide sufficient blood flow so the person can enjoy a more normal life. In the development of an implantable heart pump there is a continuing need to provide an acceptable coupling for mechanically connecting a rigid or semi-rigid pump to a flexible cannula.
Mechanical couplings for heart pumps involve several serious engineering issues. First, the coupling joint obviously has to be leak-free to prevent blood seepage. Second, the natural tendency of blood to clot at surface discontinuities and interface joints can allow the junction interface to act as a clot initiation site where formed clots could be shed into the blood stream causing serious medical complications. Sometimes, the clot can continue to grow to the point of seriously restricting pump outflow. Third, the joint must maintain its integrity for the literally millions of impulse pressure cycles that, though small, could cause a coupling to work loose. Fourth, it is desirable to make the joint easily separable, for example to accommodate a pump changeout, as well as allow the joint to be made in an operating room to better accommodate the sterilization and cannula treatment processes.
Previously, pumps were joined to a flow cannula by simply inserting the pump tube into the outlet cannula and using a standard hose clamp to secure the tube in place. This was usually adequate because the pumps themselves were relatively short-term, and were mounted external to the body. However, as technical advances resolved problems in the pumps, the "hose clamp" technique has quickly become unsatisfactory, requiring an advance coupling that can be implanted.
Existing couplings simply were not compatible with the medical protocol required for making a fully implantable pump. One of the biggest shortcomings of previous methods is the inherent tendency of blood to form clots at the pump-to-cannula interface joint site once formed, the clots can shed into the blood stream causing other serious medical complications, and occasionally the clots can grow to the point of seriously blocking the blood flow.